With Help of Variable Refrigerant Flow, 54-Year-Old School Becomes Green Lab

System is one of the country's most energy-efficient

By MITSUBISHI ELECTRIC | Sep 01, 2010

Named for the city's first Parent Teacher Association president, the Minnie Howard campus of T.C. Williams High School in Alexandria, Va., has been helping ninth-grade students transition from middle school to senior high school since 1993.

In 2008, Alexandria City Public Schools hired the Leesburg, Va., office of Hayes Large Architects LLP and Leesburg-based B2E Consulting Engineers to help turn the Minnie Howard campus into a laboratory for green-building technologies that could be implemented districtwide.

Hayes Large and B2E devised an innovative package of technologies to form one of the most energy-efficient systems in the country. This includes a creative combination of solar and ground-source geothermal energy to significantly lower heating and cooling costs, a water-source variable-refrigerant-flow (VRF) zoning HVAC system to simultaneously cool and heat the building, water-source heat pumps, solar heat exchangers, low-flow plumbing fixtures, and tubular skylights to bring sunlight to classrooms, corridors, and bathrooms.

Synchronizing all of these sophisticated technologies was a challenge.

Forty-two solar collector panels were placed in front of the school to provide active solar water heating and serve as a sun shade, reducing glare and cooling costs. For the new geothermal system, a field of 60 wells was drilled 300 ft beneath the school parking lot.

Well drilling began in April 2009. General contractor Caldwell and Santmyer Inc. of Berryville, Va., first removed the building’s 50-year-old HVAC system, which included two locomotive-sized boilers and chillers. Caldwell and Santmyer brought in Shapiro & Duncan Inc. of Rockville, Md., to install six Mitsubishi Electric water-source VRF zoning units next to the backup boilers, solar heat exchanger, and makeup outside-air unit. Shapiro & Duncan also set up the complex plumbing network, which connected 8,000 ft of piping joining the geothermal closed-loop water system to six Mitsubishi WR2-Series inverter-driven units.

The W-Series units fit into the mechanical room’s tight spaces.

"The school went from an antiquated chiller that was keeping water at 40 degrees and two huge, inefficient boilers maintaining 180-degree water all the time—even if it wasn’t needed—to a variable-speed condensing unit coupled to a geothermal well system that only runs if an indoor air handler needs cooling or heating," Chris Ott, project manager for Shapiro & Duncan, said. "Add to this the ability to cool and heat simultaneously and to zone with multiple condensing units—another energy-saving milestone."

Ott was impressed with the W-Series system's use of water as a heat-exchange medium and the use of the W-Series system in conjunction with the geothermal wells.

"It was a very logical solution for energy conservation," Ott said. "I also like the reduced cost of labor and materials needed for installation because Mitsubishi is the only two-pipe system in the industry. The installation was hassle-free, and the system started up the very first time with no glitches. When you consider there are 8,000 ft of piping, that’s amazing."

For Design Solutions author guidelines, call Scott Arnold, executive editor, at 216-931-9980, or write to him at scott[email protected].